Catalytic Conversion of Alcohols. 13. Alkene Selectivity with TiO2 Catalysts

In conversion of secondary alcohols at 200/sup 0/-265/sup 0/C, the anatase form of Ti0/sub 2/, both air- and hydrogen-pretreated, showed up to 99Vertical Bar3< selectivity for dehydration to alkenes, and the alkene isomer distributions resembled those observed over alumina catalysts, e.g., approx. 41-52Vertical Bar3< of the cis-2 isomer from 2-pentanol and 57-66Vertical Bar3< from 4-methyl-2-pentanol, but only 7-9Vertical Bar3< from 4,4-dimethyl-2-pentanol (DMP), which yielded 56-60Vertical Bar3< of 1-octene. The cis/trans 2-alkene ratio was 0.28:1 for DMP vs. 2:1 and more for 2-pentanol or 2-octanol. Anatase was also a selective catalyst for dehydration of 2-methylcyclohexanol, especially in the conversion of the pure cis-alcohol, but did not catalyze the cis-trans isomerization, suggesting an anti-elimination mechanism. For the conversion of alcohols, anatase resembled hafnia but differed markedly from zirconia and thoria. The rutile form of TiO/sub 2/, particularly when hydrogen-pretreated, was considerably more active for dehydrogenation than for dehydration of 2-octanol, and was more selective for 1-alkenes than anatase.